1. Field of the Invention
The invention relates in general to magnetic gauges and, in particular, to semi-releasable magnetic tools.
2. Description of the Prior Art
Magnetic chucks of various designs are well known and widely used. See, for example, Esposito U.S. Pat. No. 4,413,417 (an adjustable toolmakers square is held to the table of a machine tool by means of a conventional magnetic chuck); Pignataro U.S. Pat. No. 4,023,267 (a magnetic chuck of the interlocking finger type); Matsuhashi U.S. Pat. No. 4,468,649 (a switchable permanent magnetic chuck with slidably opposed poles, the sliding of which moves the chuck between magnetically excited and non-excited states); and Baermann U.S. Pat. No. 4,055,824 (a permanent magnet holding device in which the rotation of a magnetized wheel switches the device between the energized and non-energized configurations). Switching between the energized and non-energized positions in these devices is generally accomplished by slidably or rotatably moving like poles to either adjacent or opposed proximity. Various rotary magnetic switches operating on about the same or a related principle have been proposed. See, for example, Iwasaki U.S. Pat. No. 4,393,363; Wang U.S. Pat. No. 5,525,950; Levesque U.S. Pat. No. 2,280,437; and Hernandaz U.S. Pat. No. 4,470,032. The positioning of permanent magnets between ferrous pole plates where the pole plates then magnetically attach themselves to a ferrous workpiece is known. See, for example, Schloerb et al. U.S. Pat. No. 4,475,026; and Vidmar U.S. Pat. No. 5,491,907.
Various magnetic clamps for holding parts in a desired configuration while they are assembled together by welding have been proposed. For example, a non-switchable commercially available magnetic angle gauge permits the positioning and magnetic holding of workpieces in 90 and 45 degree positions. Once securely in position, this prior device is difficult to remove from the workpieces. This interferes with the intended use of the angle gauge. Typically, an operator needs to adjust the workpieces to accurately position them. This adjusting is preferably done by hand so as to avoid damaging the workpieces, and to achieve a high degree of accuracy. Where the magnetic angle gauges hold the workpieces too strongly, tools, such as hammers, must be used to overcome the strength of the magnetic forces. Accuracy is likely to suffer, and there is a risk of damaging the parts and the gauge. Removal of a non-switchable angle gauge from the finished part may also require the use of more force than is good for either the part or the angle gauge.
These and other difficulties of the prior art have been overcome according to the present invention.